Provocative question 9 asks: What are the molecular and/or cellular mechanisms that underlie the development of cancer therapy-induced severe adverse sequelae? We respond that untreatable, irreversible neurologic deficits due to cancer chemotherapy constitute a major unmet medical need for cancer patients and cancer survivors. In particular, chemotherapy-induced peripheral neuropathy (CIPN), with deficits in tactile sensation and motor function, affect many cancer patients treated with cytotoxic chemotherapies. These neurologic deficits often limit the doses of chemotherapy that can be used, and cause a major and often permanent impediment to quality of life in cancer patients and survivors. We do not yet understand the underlying mechanism for chemotherapy-induced axonal degeneration, nor do we have any way of effectively treating the resultant neuropathy. Empirical clinical trials for potential therapies have been disappointing. Therefore, to provide a solid basis to develop therapeutics it is imperative to understand the mechanistic process by which chemotherapies cause CIPN. The proposed studies will define the molecular mechanism of CIPN and initiate novel therapeutic approaches for these dire consequences of treatment. Our study plan focuses primarily on neuropathy caused by the chemotherapeutic agent, paclitaxel. Paclitaxel and related compounds are essential for effective chemotherapies for breast, ovarian and other cancers, and the majority of the more than 100,000 patients treated each year with paclitaxel experience symptoms of neuropathy. In preliminary studies using in vivo models and specialized in vitro compartmented cultures to study paclitaxel-induced degeneration of sensory neurons, we have shown that paclitaxel acts directly on axons to initiate degeneration, and that paclitaxel reduces the intracellular level of Bclw (aka Bcl2l2), a protein essential for the lifelong preservation of sensory axons. Strikingly we find that Bclw differs from its closely related family members, Bcl2 and BclxL, in that only Bclw is altered by doses of chemotherapies that cause axonal degeneration, and only Bclw can prevent axonal degeneration caused by paclitaxel. The proposed studies will elucidate the mechanisms whereby paclitaxel and other chemotherapies affect Bclw expression, and how Bclw prevents chemotherapy induced axonal degeneration. Our preliminary studies suggest the exciting possibility that Bclw-mimetics may provide the basis for designing new therapies that limit or reverse neurologic chemotherapy-induced toxicity, much as leucovorin rescue is used to limit and prevent toxicity from methotrexate or as Neulasta is used to alleviate chemotherapy induced bone marrow toxicity.